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9780521704632c12 CUFX213A/Peck 9780521618168 December 28, 2007 12:15
12 SympathomimeticsKinetics
Dobutamine is only administered intravenously. It is rapidly metabolized by COMT
to inactive metabolites that are conjugated and excreted in the urine. It has a half-life
of 2 minutes.Dopexamine
Dopexamine is a synthetic analogue of dopamine.Presentation and uses
Dopexamine is presented as 50 mg in 5 ml (at pH 2.5) for intravenous use. It is
used to improve cardiac output and improve mesenteric perfusion (dose range
0.5–6μg.kg−^1 .min−^1 ).Mechanism of action
Dopexamine stimulatesβ 2 -adrenoceptors and dopamine (D 1 )receptors and may
also inhibit the re-uptake of noradrenaline. It has only minimal effect on D 2 and
β 1 -adrenoceptors, and no effect onα-adrenoceptors.Effects
Cardiovascular – while it has positive inotropic effects (due to cardiacβ 2 -receptors),
improvements in cardiac output are aided by a reduced afterload due to peripheral
β 2 stimulation, which may reduce the blood pressure. It produces a small increase
in coronary blood flow and there is no change in myocardial oxygen extraction.
The alterations in heart rate are varied and it only rarely precipitates arrhythmias.
Mesenteric and renal – blood flow to the gut and kidneys increases due to an
increased cardiac output and reduced regional vascular resistance. Urine output
increases. It may cause nausea and vomiting.
Respiratory – bronchodilation is mediated viaβ 2 stimulation.
Miscellaneous – tremor and headache have been reported.Kinetics
Dopexamine is cleared rapidly from the blood and has a half-life of 7 minutes.Salbutamol
Salbutamol is a synthetic sympathomimetic amine with actions mainly atβ 2 -adreno-
ceptors.Presentation and uses
Salbutamol is presented as a clear solution containing 50–500μg.ml−^1 for intra-
venous infusion after dilution, a metered dose inhaler (100μg) and a dry powder
(200–400μg) for inhalation, a solution containing 2.5–5 mg.ml−^1 for nebulization,